Overview

Brief Summary

Species Overview

Dinophysis acuminata is an armoured, marine, planktonic dinoflagellate species. It is a toxic species associated with DSP events and is commonly found in coastal waters of the northern Atlantic and Pacific Oceans.

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Thecal Plate Description

The epitheca is slightly convex and inclined ventrally (Figs. 1-4). Made up of four plates, it is not visible in lateral view.

The cingulum is made up of four unequal plates, and is bordered by two well-developed lists: an anterior cingular list (ACL), often with ridges, and a smooth posterior cingular list (PCL) (Fig. 1). The dorsal end of the cingulum is concave, strongly inclined and (Figs. 1, 6).

The sulcus is comprised of four irregularly shaped plates. The flagellar pore is housed in the sulcal area. The LSL, supported by three ribs, is rather narrow and often sculptured with reticulated ribs, lines and areolae. The third rib on the left sulcal list is the longest, and is usually strongly curved posteriorly (Figs. 1, 4, 6). Sulcal plate development is highly variable in this species.

The hypotheca, with four large plates, comprises the majority of the cell. The dorsal margin is more or less evenly convex (Figs. 1, 2, 4). The ventral margin is rarely convex; it is generally oblique and flat (Figs. 2-5). The antapex is ventrally off-center (Figs. 2-5).

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Taxonomic Description

Species in this genus are laterally compressed with a small, cap-like epitheca and a much larger hypotheca (dorso-ventral depth of epitheca is 1/3 to 1/2 of hypotheca). The shape of the cell in lateral view is the most important criterion used for identification. However, size and shape varies considerably in this species.

Cells of Dinophysis acuminata are small to medium, almost oval or elliptical in shape (Figs. 1-5). The shape can vary from rotund to long and narrow in lateral view. A well-developed left sulcal list (LSL) extends beyond the midpoint of the cell (1/2 to 2/3 of cell length (Figs. 1-3). The antapex is rounded, and cells are commonly found with two to four small knob-shaped posterior protrusions; sometimes well-developed and sometimes not (Figs. 2-5).

The thick thecal plates are covered with prominent circular areolae, each with a pore (Fig. 2). These markings can vary depending on the age of the cell. The variations can range from only pores (Fig. 3), to depressions with scattered pores (Fig. 1), to depressions each with a pore, to areolae each with a pore (Fig. 2). Pores are not found in the megacytic zone (Fig. 3). Cell size ranges: 38-58 µm in length and 30-40 µm in dorso-ventral width widest near middle of cell.

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Look Alikes

Species Comparison

D. acuminata can be confused with D. sacculus, D. norvegica, D. ovum and D. punctata, but is most often misidentified as D. sacculus. The major difference between D. acuminata and D. sacculus is the shape of the large hypothecal plates: in D. acuminata they are shorter, more convex dorsally and often more slender posteriorly; whereas, in D. sacculus they are long and sack-like. D. acuminata also exhibits more pronounced thecal areolation and sulcal list ornamentation, but these are variable features. Since these two species rarely occur in the same area with the same importance, the possibility of misidentification is reduced. Surface thecal ornamentation in this species is similar to D. sacculus.

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Ecology

Habitat

Habitat and Locality

Populations of Dinophysis acuminata are distributed widely in temperate waters. They are most common and abundant in coastal waters of the northern Atlantic and Pacific Oceans, especially eutrophic areas.

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General Ecology

Ecology

D. acuminata is a planktonic toxic bloom-forming species. The most extensive blooms have been reported from the summer and fall months. Blooms have been reported from many parts of the world; however, they have been particularly extensive with cell concentrations less than 40,000 cells/L. Blooms are often associated with toxicity of shellfish. Jacobson and Andersen (1994) found a high number of food vacuoles in cells of Dinophysis acuminata and deduced that mixotrophy is an important aspect of its biology. They speculate that this species feeds by way of a peduncle (myzocytosis), the feeding mode used by the heterotrophic species Dinophysis rotundata and D. hastata. The peduncle, the proposed feeding apparatus, passes through the cytostomal opening in the theca when the cell is feeding.

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Physiology and Cell Biology

Physiology

Toxicity

D. acuminata is a toxic species that has been found to produce okadaic acid (OA) causing diarrhetic shellfish poisoning (DSP). Toxicity can vary considerably among seasons and areas where it blooms. This species can cause shellfish toxicity at very low cell concentrations (as low as 200 cells/L). Hoshiai et al. (1997), however, reported a case of nontoxic mussels in Kesennuma Bay, northern Japan, in the presence of high concentrations of D. acuminata cells.

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Wikipedia

Dinophysis acuminata

Dinophysis acuminata is a marine plankton species belonging to the phylum Dinoflagellate that is found in coastal waters of the north Atlantic and Pacific oceans.[1] The Dinophysis genus includes both phototrophic and heterotrophic species. D. acuminata is one of several phototrophic species of Dinophysis classed as toxic, as they produce okadaic acid which can cause diarrhetic shellfish poisoning (DSP). Okadiac acid is taken up by shellfish and has been found in the soft tissue of mussels and the liver of flounder species. When contaminated animals are consumed, they cause severe diarrhoea. D. acuminata blooms are constant threat to and indication of diarrhoeatic shellfish poisoning outbreaks.[2][3][4]

Contents

Dinophysis acuminata is an oval-shaped protist. It measures 30-35 μm in length and 38-58 μm in diameter. The body is reddish-brown in colour and is covered with an armour-like covering called theca, which is made up of cellulose. The anterior end has a crown-like platform, which is the smaller epitheca; while the posterior is simply rounded constituting a larger hypotheca. The cell has two flagella for locomotion. Reproduction is by simple binnary fission. In lateral view D. acuminata cells are irregularly egg-shaped, dorsally convex and have large hypothecal plates with a more or less oval shape. The dorsal contour is always more strongly convex than the ventral one. Compared to other species of Dinophysis, D. acuminata has a more straight ventral margin and larger left sulcal lists with more prominent ribs. The nucleus is prominently at the centre of the cell. The unusual feature of the cell is that it contains reddish-brown chloroplast.[1]

The taxonomic identification of Dinophysis species is largely based on cell contouring, size and shape of their large hypothecal plates and the shape of their left sulcal lists and ribs. When viewed laterally species in the Dinophysis genus are laterally compressed with a cap-like epitheca and a much larger hypotheca although the size and shape of these species varies greatly due to their polymorphic life cycle. Due to the morphological variability of Dinophysis species identification can be hard, especially when two species (D. acuminata and D. sacculus) co-exist. For this reason the term "D. acuminata complex" was coined to label a group of co-existing species difficult to discriminate.[8]

Dinophysis acuminata is basically a heterotroph feeding on the ciliate Myrionecta rubra. M. rubra in turn feeds on green algae that contain plastids. (The endosymbiont is used by the ciliate for its own photosynthesis.)[9] Microscopic observations of live cells using established cultures revealed that D. acuminata uses a peduncle, extending from the flagellar pore, to extract the cell contents of the marine ciliate M. rubra. After about 1 minute the trapped M. rubra becomes immobile after which the D. acuminata slowly consumes the ciliate, over 1–2 hours, filling its vacuoles with the ciliate's cytoplasm.[8] The algal plastids are not destroyed by D. acuminata but use it for its own photosynthesis, thereby becoming an autotroph. However, unlike its prey M. ruba, it is not clear whether D. acuminata uses the plastids permanently or temporarily.[10][11]